#pragma warning(disable:4996)
#include<stdio.h>

int main() {
    double gz, sds, ss;
    scanf("%lf", &gz);
    if (gz <= 1600)
        sds = 0;
    else if (gz > 1600 && gz <= 2500)
        sds = 0.05;
    else if (gz > 2500 && gz <= 3500)
        sds = 0.1;
    else if (gz > 3500 && gz <= 4500)
        sds = 0.15;
    else
        sds = 0.2;
    ss = sds * (gz - 1600);
    printf("%.2f\n", ss);
    return 0;
}